Abstract

CAG trinucleotide repeat length in the nuclear polymerase gamma gene (POLγ) has been shown to be associated with men with reduced fertility. The present study investigated the frequency of CAG repeat length genotypes and three exonuclease motifs of the POLγ in relation to the frequency of mitochondrial nucleotide substitutions. DNA from semen samples of 93 normozoospermic men and 192 non-normozoospermic men was isolated and the specific regions of the genes were amplified by polymerase chain reactions (PCR) and sequenced to identify mutations. The genotypic frequencies of pooled POLγ CAG repeat lengths, =10/≠10 heterozygotes and ≠10/≠10 homozygotes, were significantly different between normozoospermic and non-normozoospermic men (p < 0.05), with non-normozoospermic men having a slightly higher frequency of the =10/=10 genotypes. The allelic frequency for =10 is 0.79 and ≠10 is 0.21 for normozoospermic men and 0.85 and 0.15, respectively, for non-normozoospermic men (p < 0.025). There was no mutation detected in the exonuclease motifs in all the samples tested. Eighty normozoospermic and 124 non-normozoospermic semen samples were analysed for nucleotide substitutions in mitochondrial genes by PCR and sequencing. Heteroplasmic mutations were found in one azoospermic man, four asthenozoospermic men and two normozoospermic men. Only one asthenozoospermic man was heterozygous for the POLγ genotype. Of the 17 men with non-synonymous nucleotide substitutions, 14 were homozygous for the POLγ genotype. Non-normozoospermic men had twice as many nucleotide substitutions than normozoospermic men. However, there were no significant differences in the frequencies of nucleotide substitution and POLγ genotypes in the two groups of men.